Tidal Bay has been allotted top weight of 11st 10lb in the John Smith's Grand National at Aintree on April 6.

The Paul Nicholls-trained 12-year-old has been in tremendous form this season, finishing second in the Hennessy at Newbury to Gold Cup favourite Bobs Worth and then winning the Lexus Chase at Leopardstown.

He has an official British Horseracing Authority mark of 171 but has been rated on 162 by official handicapper Phil Smith, who is allowed to use his discretion in framing the National weights.

Nicholls won the National for the first time last year when the now-retired Neptune Collonges edged out Sunnyhillboy in a thrilling finish, and his team is further bolstered by Becher Chase runner-up Join Together (10st 12lb), and a pair part-owned by Sir Alex Ferguson in What A Friend (11st 5lb) and Harry The Viking (10st 2lb).

Tidal Bay is owned by Andrea and Graham Wylie, who also have leading contenders On His Own (10st 10lb) and Prince De Beauchene (11st 3lb), both of whom are trained by Willie Mullins in Ireland.

A strong Irish-trained entry of 31 features the Ted Walsh-trained pair of Seabass (11st 2lb) and Colbert Station (10st 11lb).

Seabass carried 4lb less when third 12 months ago, and Walsh, speaking before seeing the full list of weights, said: "I don't know how Seabass can get over 11st this year if Tidal Bay is rated 171 and my horse is rated 154.

"Whatever Phil Smith does, he does - it is immaterial to me and I can't change it. You don't have to be a great mathematician to subtract 54 from 71."

Seabass returned to the racecourse for the first time since his gallant Aintree effort to run a staying-on second over two miles in a hurdle race at Fairyhouse last week.

Walsh said: "Seabass will run somewhere in the next three weeks to a month. There is just over seven weeks to Liverpool so I would like to get a run into him. The Bobbyjo Chase at Naas and the Racing Plus Chase at Kempton are possible targets."

Walsh, who won the National in 2000 with Papillon, said of Colbert Station: "Like Seabass, Colbert Station will possibly have one more run. I have no idea where he will go at this stage as he only recently ran. I would also be looking at running him in three weeks to a month's time, which will be ideal timing for the National."

"I don't know how Seabass can get over 11st this year if Tidal Bay is rated 171 and my horse is rated 154. Whatever Phil Smith does, he does - it is immaterial to me and I can't change it. You don't have to be a great mathematician to subtract 54 from 71."Ted Walsh

The JP McManus-owned Colbert Station won a valuable handicap chase at Leopardstown over Christmas and followed up over hurdles at Punchestown, ridden on both occasions by Tony McCoy on testing ground.

Walsh said: "I wouldn't be worried about the ground for Colbert Station as it is never anything worse than good jumping ground at Aintree. He has 10st 6lb in the Racing Plus Chase at Kempton and is 3lb higher in England than he is in Ireland, which makes him worse off with Seabass in England."

Seabass was ridden by Walsh's daughter Katie last year, when she achieved the highest finishing place yet by a lady rider in the National. His son Ruby would appear to have a number of choices, while McCoy is retained rider for McManus.

On the subject of jockey plans, Walsh said: "The question of who will ride both horses is the least of my worries at the moment. My only worry is the two horses arrive at Liverpool in good form, healthy and well. Who rides them is a question for another day. I am not even thinking about it and there is no pressure on anybody.

"Nobody has to make their mind up until I have to declare for the race - I don't need to know if Tony McCoy is available or Ruby Walsh is available until they make their minds up, and at the declaration stage will do for me."

Jonjo O'Neill's Sunnyhillboy, also owned by McManus, has 11st this year compared to 10st 5lb in 2012, while the Donald McCain-trained Ballabriggs, successful in 2011, is another on 11st, the same weight as he carried to victory under Jason Maguire.

McCain said: "That weight is fine for Ballabriggs and it will be grand if the top horse (Tidal Bay) runs because then we will have a lovely racing weight. He has come out of his race at Warwick OK. He will go to Kelso for the Premier Chase, as he has done for the past two years, and then on to Aintree."